Communication system in digital television

ABSTRACT

A VSB communication system or transmitter for processing supplemental data packets with MPEG-II data packets includes a VSB supplemental data processor and a VSB transmission system. The VSB supplemental data processor includes a Reed-Solomon coder for coding the supplemental data to be transmitted, a repetition coder for inserting repetion data to an intereaved supplemental data for generating a predefined sequence, a header inserter for inserting an MPEG header to the supplemental data having the repetion code inserted therein, a multiplexer for multiplexing an MPEG data coded with the supplemental data having the MPEG header added thereto in a preset multiplexing ratio and units. The output of the multiplexer is provided to an 8T-VSB transmission system for modulating a data field from the multiplexer and transmitting the modulated data field to a VSB reception system.

CROSS REFERENCE TO RELATED ART

This application claims the benefit of Korean Patent Application No.2001-22200, filed on Apr. 25, 2001, which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a digital television transmissionsystem, and more particularly, to a 8T-VSB (Vestigial Sideband)transmission system for transmitting supplemental data in addition toMPEG data and to a signal format for the VSB transmission system.

2. Description of the Related Art

The United States of America has employed ATSC 8T-VSB (8Trellis-Vestigial Sideband) as a standard since 1995, and has beenbroadcasting in the ATSC 8T-VSB since the later half of 1998. SouthKorea also has employed the ATSC 8T-VSB as a standard. South Koreastarted test broadcasting in May 1995, and has since August 2000 put inplace a regular test broadcasting system. The advancement of technologyallows the transmission of digital television (DTV) in the same 6 MHzbandwidth currently used by NTSC.

FIG. 1 illustrates a block diagram of a related art ASTC 8T-VSBtransmission system (“VSB transmission system”). The VSB transmissionsystem 16 generally comprises a data randomizer 1, Reed-Solomon coder 2,data interleaver 3, Trellis coder 4, multiplexer 5, pilot inserter 6,VSB modulator 7 and RF converter 8.

Referring to FIG. 1, there is a data randomizer 1 for receiving andmaking random MPEG data (video, audio and ancillary data). The datarandomizer 1 receives the MPEG-II data output from an MPEG-II encoder.Although not shown in FIG. 1, the MPEG-II encoder takes baseband digitalvideo and performs bit rate compression using the techniques of discretecosine transform, run length coding, and bi-directional motionprediction. The MPEG-II encoder then multiplexes this compressed datatogether with pre-coded audio and any ancillary data that will betransmitted. The result is a stream of compressed MPEG-II data packetswith a data frequency of only 19.39 Mbit/Sec. The MPEG-II encoderoutputs such data to the data randomizer in serial form. MPEG-II packetsare 188 bytes in length with the first byte in each packet always beingthe sync or header byte. The MPEG-II sync byte is then discarded. Thesync byte will ultimately be replaced by the ATSC segment sync in alater stage of processing.

In the VSB transmission system 16, the 8-VSB bit stream should have arandom, noiselike signal. The reason being that the transmitted signalfrequency response must have a flat noise-like spectrum in order to usethe allotted 6 MHz channel space with maximum efficiency. Random dataminimizes interference into analog NTSC. In the data randomizer 1, eachbyte value is changed according to known pattern of pseudo-random numbergeneration. This process is reversed in the VSB receiver in order torecover the proper data values.

The Reed-Solomon coder 2 of the VSB transmission system 16 is used forsubjecting the output data of the data randomizer 1 to Reed-Solomoncoding and adding a 20 byte parity code to the output data. Reed Solomonencoding is a type of forward error correction scheme applied to theincoming data stream. Forward error correction is used to correct biterrors that occur during transmission due to signal fades, noise, etc.Various types of techniques may be used as the forward error correctionprocess.

The Reed-Solomon coder 2 takes all 187 bytes of an incoming MPEG-II datapacket (the sync or header byte has been removed from 188 bytes) andmathematically manipulates them as a block to create a digital sketch ofthe block contents. This “sketch” occupies 20 additional bytes which areadded at the tail end of the original 187 byte packet. These 20 bytesare known as Reed-Solomon parity bytes. The 20 Reed-Solomon parity bytesfor every data packet add redundancy for forward error correction of upto 10 byte errors/packet. Since Reed-Solomon decoders correct byteerrors, and bytes can have anywhere from 1 to 8 bit errors within them,a significant amount of error correction can be accomplished in the VSBreceiver. The output of the Reed-Solomon coder 2 is 207 bytes (187 plus20 parity bytes).

The VSB receiver will compare the received 187 byte block to the 20parity bytes in order to determine the validity of the recovered data.If errors are detected, the receiver can use the parity bytes to locatethe exact location of the errors, modify the corrupted bytes, andreconstruct the original information.

The data interleaver 3 interleaves the output data of the Reed-Solomoncoder 2. in particular, the data interleaver 3 mixes the sequentialorder of the data packet and disperses or delays the MPEG-II packetthroughout time. The data interleaver 3 then reassembles new datapackets incorporating small sections from many different MPEG-II(pre-interleaved) packets. The reassembled packets are 207 bytes each.

The purpose of the data interleaver 3 is to prevent losing of one ormore packets due to noise or other harmful transmission environment. Byinterleaving data into many different packets, even if one packet iscompletely lost, the original packet may be substantially recovered frominformation contained in other packets.

The VSB transmission system 16 also has a trellis coder 4 for convertingthe output data of the data interleaver 3 from byte form into symbolform and for subjecting it to trellis coding. Trellis coding is anotherform of forward error correction. Unlike Reed-Solomon coding, whichtreated the entire MPEG-II packet simultaneously as a block, trelliscoding is an evolving code that tracks the progressing stream of bits asit develops through time.

The trellis coder 4 adds additional redundancy to the signal in the formof more (than four data levels, creating the multilevel (8) data symbolsfor transmission. For trellis coding, each 8-bit byte is split up into astream of four, 2-bit words. In the trellis coder 4, each 2-bit inputword is compared to the past history of previous 2-bit words. A 3-bitbinary code is mathematically generated to describe the transition fromthe previous 2-bit word to the current one. These 3-bit codes aresubstituted for the original 2-bit words and transmitted as the eightlevel symbols of 8-VSB. For every two bits that enter the trellis coder4, three bits come out.

The trellis decoder in the VSB receiver uses the received 3-bittransition codes to reconstruct the evolution of the data stream fromone 2-bit word to the next. In this way, the trellis coder follows a“trail” as the signal moves from one word to the next through time. Thepower of trellis coding lies in its ability to track a signal's historythrough time and discard potentially faulty information (errors) basedon a signal's past and future behavior.

A multiplexer 5 is used for multiplexing a symbol stream from thetrellis coder 4 and synchronizing signals. The segment and the fieldsynchronizing signals provide information to the VSB receiver toaccurately locate and demodulate the transmitted RF signal. The segmentand the field synchronizing signals are inserted after the randomizationand error coding stages so as not to destroy the fixed time andamplitude relationships that these signals must possess to be effective.The multiplexer 5 provides the output from the trellis coder 4 and thesegment and the field synchronizing signals in a time division manner.

An output packet of the data interleaver 3 comprises the 207 bytes of aninterleaved data packet. After trellis coding, the 207 byte segment isstretched out into a baseband stream of 828 eight level symbols. Thesegment synchronizing signal is a four symbol pulse that is added to thefront of each data segment and replaces the missing first byte (packetsync byte) of the original MPEG-II data packet. The segmentsynchronizing signal appears once every 832 symbols and always takes theform of a positive-negative-positive pulse swinging between the +5 and−5 signal levels.

The field synchronizing signal is an entire data segment that isrepeated once per field. The field synchronizing signal has a known datasymbol pattern of positive-negative pulses and is used by the receiverto eliminate signal ghosts caused by poor reception.

The VSB transmission system 16 also has the pilot inserter 6 forinserting pilot signals into the symbol stream from the multiplexer 5.Similar to the synchronizing signals described above, the the pilotsignal is inserted after the randomization and error coding stages so asnot to destroy the fixed time and amplitude relationships that thesesignals must possess to be effective.

Before the data is modulated, a small DC shift is applied to the 8T-VSBbaseband signal. This causes a small residual carrier to appear at thezero frequency point of the resulting modulated spectrum. This is thepilot signal provided by the pilot inserter 6. This gives the RF PLLcircuits in the VSB receiver something to lock onto that is independentof the data being transmitted.

After the pilot signal has been inserted by the pilot inserter 6, theoutput is subjected to a VSB modulator 7. The VSB modulator 7 modulatesthe symbol stream from the pilot inserter 6 into an 8 VSB signal of anintermediate frequency band. The VSB modulator 7 provides a filtered(root-raised cosine) IF signal at a standard frequency (44 Mhz in theU.S.), with most of one sideband removed.

In particular, the eight level baseband signal is amplitude modulatedonto an intermediate frequency (IF) carrier. The modulation produces adouble sideband IF spectrum about the carrier frequency. The totalspectrum is too wide to be transmitted in the assigned 6 MHz channel.

The sidelobes produced by the modulation are simply scaled copies of thecenter spectrum, and the entire lower sideband is a mirror image of theupper sideband. Therefore using a filter, the VSB modulator discards theentire lower sideband and all of the sidelobes in the upper sideband.The remaining signal (upper half of the center spectrum) is furthereliminated in one-half by using the Nyquist filter. The Nyquist filteris based on the Nyquist Theory, which summarizes that only a ½ frequencybandwidth is required to transmit a digital signal at a given samplingrate.

Finally, there is a RF (Radio Frequency) converter 8 for converting thesignal of an intermediate frequency band from the VSB modulator 7 into asignal of a RF band signal, and for transmitting the signal to areception system through an antenna 9.

The foregoing VSB communication system is at least partially describedin U.S. Pat. Nos. 5,636,251, 5,629,958 and 5,600,677 by Zenith Co. whichare incorporated herein by reference. The 8T-VSB transmission system,which is employed as the standard digital TV broadcasting in NorthAmerica and South Korea, was developed for the transmission of MPEGvideo and audio data. As technologies for processing digital signalsdevelop and the use of the Internet increases, the trend currently is tointegrate digitized home appliances, the personal computer, and theInternet into one comprehensive system.

Therefore, in order to satisfy the variety of the demands of users,there is a need to develop a communication system that facilitates theaddition and transmittal of a variety of supplemental data to the videoand audio data through the digital broadcasting channel. It is predictedthat the use of supplemental data broadcasting may require PC (PersonalComputer) cards or portable appliances, with simple indoor antennas.

However, there can be a substantial reduction of signal strength due towalls and nearby moving bodies. There also can be ghost and noise causedby reflective waves, which causes the performance of the signal of thesupplemental data broadcasting to be substantially poor. Supplementaldata broadcasting is different from general video and audio data in thatit requires a lower error ratio in transmission. For general video andaudio data, errors imperceptible to the human eye or ear areinconsequential. In contrast, for supplemental data, even one bit oferror in the supplemental data (which may include program executionfiles, stock information, and other similar information) may cause aserious problem. Therefore, the development of a communication systemthat is more resistant to the ghost and noise occurring on the channelis absolutely required.

In general, the supplemental data is transmitted by a time divisionsystem on a channel similar to the MPEG video and audio data. After theincorporation of digital broadcasting, there has already been awidespread emergence in the home appliance market of receivers equippedto receive ATSC VSB digital broadcast signals. These products receiveMPEG video and audio data only. Therefore, it is required that thetransmission of supplemental data on the same channel as the MPEG videoand audio data has no adverse influence on the existing receivers thatare equipped to receive ATSC VSB digital broadcasting.

The above situation is defined as ATSC VSB backward compatibility, andthe supplemental data broadcasting system must be a system that isbackward-compatible with the ATSC VSB communication system.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a VSB communicationsystem, and a signal format for the VSB communication system thatsubstantially obviates one or more of the problems due to thelimitations and disadvantages of the related art.

An object of the present invention is to provide an ATSC VSBtransmission system, which can transmit the present MPEG video and audiodata together with supplemental data.

Another object of the present invention is to provide an ATSC VSBtransmission system that is more robust to ghost and noise.

A further object of the present invention is to provide a new ATSC VSBtransmission system that is fully backward-compatible with a related artATSC VSB transmission system.

A still further object of the present invention is to provide atransmission data format that is suitable to an ATSC VSB transmissionsystem which is robust to ghost and noise.

Additional features and advantages of the invention will be set forth inthe description that follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, the VSBtransmitter for use with an MPEG data signal and a supplemental datasignal comprises a VSB supplemental data processor and a 8T-VSBtransmission system. The VSB supplemental data processor comprises aforward error correction coder that codes the supplemental data signal;repetition coder for inserting repetition bits to supplemental datasignal and outputting repetition data; a header inserter for inserting aheader to the supplemental data signal having the repetition datainserted therein; and a multiplexer for multiplexing the MPEG datasignal and the supplemental data signal having the header insertedthereto in at least one of a predetermined multiplexing ratio and unit.

The VSB transmission system is responsive to the VSB supplemental dataprocessor for modulating an output from the multiplexer to form at leastone data field comprising a plurality of segments that includes at leastone segment representing the supplemental data signal and at least onesegment representing the MPEG data signal.

According to one aspect of the present invention, the forward errorcorrection coder is a Reed-Solomon coder. The supplemental data signalincludes at least one data packet having X bytes and the Reed-Solomoncoder provides parity bytes of Y bytes, wherein a total of X and Y bytesis 184 bytes.

According to another aspect of the present invention, the headerinserter adds three bytes of header information to the data packet.Preferably ,a repetition coder repeatedly codes input 1 byte, convertsthe input 1 byte to 2 bytes, and outputs the resultant value. Thisimproves a receiving performance by widening the distance betweensymbols when a trellis coded modulator (TCM) performs coding. That is,the distance between symbols becomes wide by inputting 000, 110, 001,and 111 to the TCM with a repetition coding.

According to another aspect of the present invention, the VSBtransmitter further comprises an interleaver receiving data from theforward error correction coder and outputting to the repetition coder.The interleaver interleaves the supplemental data signal with forwarderror corrected code. Also said interleaver may omit the present of theinvention.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 illustrates a block diagram showing a conventional VSBtransmission system;

FIG. 2 illustrates a block diagram showing VSB signal constellation

FIG. 3 illustrates a block diagram showing a VSB transmitter fortransmitting supplemental and MPEG data in accordance with a preferredembodiment of the present invention;

FIG. 4 illustrates the frame architecture of a transmission data for aVSB transmission system in accordance with a preferred embodiment of thepresent invention;

FIG. 5 illustrates a diagram showing a process for multiplexingsupplemental data and MPEG data for forming a VSB data field;

FIG. 6 illustrates an example of inserting the repetition bits into thesupplemental data by the repetition coder and generating a predefineddata;

FIG. 7 illustrates a schematic diagram of a data interleaver forinterleaving supplemental data;

FIG. 8 illustrates a block diagram showing trellis coder and pre-coder

FIG. 9 illustrates an example of coding supplemental data(block size=164byte); and

FIG. 10 illustrates another example of coding supplemental data(blocksize=82 byte).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. FIG. 2 illustrates VSB signal constellation.

FIG. 3 illustrates a block diagram showing a VSB transmitter 110 for thetransmission of the supplemental and MPEG data in accordance with apreferred embodiment of the present invention. FIG. 4 illustrates theframe architecture of transmission data for a VSB transmission system inaccordance with a preferred embodiment of the present invention. FIG. 5illustrates a diagram showing a process for multiplexing supplementaldata and MPEG data for forming a VSB data field. FIG. 6 illustrates adiagram showing a process for inserting a repetition data intosupplemental data. FIG. 7 illustrates a diagram showing a datainterleaver for interleaving supplemental data. FIG. 8 illustrates ablock diagram showing trellis coder and pre-coder.

FIG. 9 illustrates a diagram showing an example of coding supplementaldata(block size=164 byte), and FIG. 10 illustrates a diagram showinganother example of coding supplemental data(block size=82 byte).

FIG. 2 illustrates a constellation shape of a VSB signal according tothe present invention. When additional data are repeatedly transmitted,4 symbols 000, 110, 001, and 111 are output. That is, one of eightsymbols 000, 001, 010, 011, 100, 101, 110, and 111 is generally outputwhen the TCM performs coding. In the present invention, one of foursymbols is output. Therefore, the distance between symbols becomes wide,thereby reducing a rate of an error occurrence.

In FIG. 3, the VSB transmitter 110 in accordance with a preferredembodiment of the present invention includes a VSB supplemental dataprocessor 100 and a VSB transmission system 16. The description of theVSB transmission system 16 is described above in connection with FIG. 1,and thus, will not be repeated. According to the preferred embodiment ofthe present invention, the VSB supplemental data processor includes aReed-Solomon coder 11, a data interleaver 12, a repetition coder 13, anMPEG header inserter 14, a multiplexer 15, an 8T-VSB transmission system16, and an antenna 17.

As shown in FIG. 3, for the transmission of the supplemental data fromthe VSB transmitter 110 (i.e., a broadcasting station) to a VSBreception system on a channel (terrestrial or cable), the VSBtransmitter 110 subjects the supplemental data to various digital signalprocesses. To provide backward compatibility of the present inventionwith existing devices, the supplemental data is preferably 164 bytepacket which will eventually be processed to be a 187 byte packet beforeentering the VSB transmission system 16. However, the size of thesupplemental data packet may be varied so long as the output of the VSBsupplemental data processor 100 is compatible with the VSB transmissionsystem 16.

In the VSB supplemental data processor 100, there is provided aReed-Solomon coder 11 for the correction of errors. The supplementaldata is coded at a Reed-Solomon coder (or R-S coder) 11. Preferably, theReed-Solomon coder 11 is used for subjecting the supplemental data toReed-Solomon coding and adding a 20 byte parity code to the output data.As described above, Reed Solomon encoding is a type of forward errorcorrection scheme applied to the incoming data stream. Forward errorcorrection is used to correct bit errors that occur during transmissiondue to signal fades, noise, etc. Various other types of error correctiontechniques known to one of ordinary skill in the art may be used as theforward error correction process.

According to the preferred embodiment, the Reed-Solomon coder 11 of theVSB supplemental data processor takes 164 bytes of an incomingsupplemental data packet and mathematically manipulates them as a blockto create a digital sketch of the block contents. The 20 additionalbytes are added at the tail end of the original 164 byte packet. These20 bytes are known as Reed-Solomon parity bytes. Since Reed-Solomondecoders of the VSB reception system correct byte errors, and bytes canhave anywhere from 1 to 8 bit errors within them, a significant amountof error correction can be accomplished in the VSB receiver. The outputof the Reed-Solomon coder 11 is preferably 184 bytes (164 bytes from theoriginal packet plus 20 parity bytes).

The VSB supplemental data processor 100 further includes the datainterleaver 12, which interleaves the output data of the Reed-Solomoncoder 11. The interleaver 12 is for interleaving the coded supplementaldata to enhance performance against burst noise. The interleaver 12 maybe omitted, if necessary.

The data interleaver 12 according to the preferred embodiment mixes thesequential order of the supplemental data packet and disperses or delaysthe supplemental data packet throughout time. The data interleaver 12then reassembles new data packets incorporating small sections from manydifferent supplemental data packets. Each one of the reassembled packetsare 184 bytes long.

As described above, the purpose of the data interleaver 12 is to preventlosing of one or more packets due to noise or other harmful transmissionenvironment. By interleaving data into many different packets, even ifone packet is completely lost, the original packet may be recovered frominformation contained in other packets. However there is a datainterleaver in the ASTC 8T-VSB transmission system, the data interleaverfor the supplemental data can be omitted if it is not required toenhance the burst noise performance of the supplemental data. For thisreason, the data interleaver 12 may not be necessary for the VSBsupplemental data processor 100.

The VSB supplemental data processor 100 also includes the repetitioncoder 13 for inserting repetition bit to an allocated region of theinterleaved (if the data interleaver 12 was present) or Reed-Solomoncoded supplemental data for generating the predefined sequence for thesupplemental data at an input terminal of a Trellis coder (shown in FIG.8). The repetition data is inserted so that the VSB reception systemreceives the supplemental data more reliably, even in a noisy multipathfading channel. An example structure of the transmission data formed bythe insertion of the repetition coder will be explained below in detailwith reference to FIG. 6.

Further referring to FIG. 3, the VSB supplemental data processor 100includes the MPEG header inserter 14 for adding an MPEG header to thesupplemental data having the repetition data inserted thereto, forbackward-compatibility with the legacy VSB reception system. Because theMPEG-II data supplied to the VSB transmission system 16 is 187 byteslong, the MPEG header inserter 14 places, preferably, three headers infront of each packet (which was 184 bytes) to form a 187 byte longpacket identical to the MPEG-II data packet.

The supplemental data having the MPEG header added thereto is providedto a multiplexer 15. The multiplexer 15 receives as inputs the processedsupplemental data from the MPEG header inserter 14 and MPEG datapackets. MPEG data packet, such as a broadcasting program (movie,sports, entertainment, or drama), coded through another path (outputfrom MPEG encoder), is received together with the supplemental data atthe multiplexer 15. Upon reception of the MPEG data and the supplementaldata, the multiplexer 15 multiplexes the supplemental data and the MPEGdata at a fixed ratio under the control of a controller defining amultiplexing ratio and unit and forwards the multiplexed data to the8T-VSB transmission system 16.

The 8T-VSB transmission system 16, which is described in detail inreference to FIG. 1, processes the multiplexed data and transmits theprocessed data to the VSB reception system through the antenna 17.

For example, the Reed-Solomon coder 11 uses a code having a block sizeN=184, a payload K=164, and an error correction capability T=10. On theother hand, as a generator polynomial of the Galois Field and theReed-Solomon coder 11, the same code as the the Reed-Solomon coder 2described with respect to FIG. 1 may be used. According to the preferredembodiment, other values of the block size N, the payload K, and theerror correction capability T may be used in the Reed-Solomon coder 11in FIG. 3. For an example, a code having N=184, K=154, and T=15 may beused, or a code having N=92, K=82, and T=5 may be used. Although theReed-Solomon code is used in the present invention, other code suitablefor error correction known to one of ordinary skill in the art may beused therein.

FIG. 4 illustrates the structure of a VSB data field used in the VSBtransmission system 100. As shown in FIG. 4, one data field has 313segments: 312 data segments 124 and one field synchronizing segment 122.The 312 data segments have data segments of the supplemental data andthe MPEG data segments. Each data segment 124A has 184 byte data, a 3byte MPEG header, and the 20 byte ATSC Reed-Solomon parity. The 3 byteMPEG header will used by the MPEG decoder in the VSB reception system.

The use of the MPEG header is explained in more detail. ISO/IEC 13818-1has a definition on an MPEG transport packet header. If a 0×47synchronization byte is removed from the MPEG transport packet header, a3 byte header is left. A PID (program identification) is defined by this3 bytes, a transport part of the MPEG decoder discards a packet if thePID of the received packet received is not valid. For example, a nullpacket PID or other reserved PID can be used. Therefore, the MPEG headerinserter 14 in FIG. 3 inserts the 3 byte header containing such a PIDinto the supplemental data packet. Therefore, the supplemental data canbe discarded at the MPEG decoder of the legacy VSB receiver.

FIG. 5 illustrates a process for multiplexing the supplemental data andthe MPEG data at the multiplexer 15 in FIG. 3. As shown in FIG. 5, thesupplemental data is multiplexed with the MPEG data in segment units.The supplemental data is multiplexed with the MPEG data in synchronousto the field synchronizing signal used for synchronizing a data framesynchronization in the VSB transmission system.

Therefore, the VSB reception system determines the multiplexinglocations of the MPEG data and the supplemental data in the field datareceived synchronous to the field synchronizing signal. The VSBreception system demultiplexes the MPEG data and the supplemental databased on the multiplexing locations. A multiplexing ratio and method formultiplexing the MPEG data and the supplemental data may vary withamounts of data thereof.

Information on the variable multiplexing method and ratio may be loadedon, for example, a reserved area of the 92 bits not used in the fieldsynchronizing signal. By retrieving and decoding such information, theVSB reception system identifies the correct multiplexing ratio andmethod from the multiplexing information contained in the fieldsynchronizing signal.

Alternatively, the multiplexing information may be inserted, not only inthe reserved area of the field synchronizing signal, but also in thedata segment of the supplemental data. As shown in FIG. 5, of the entire312 multiplexed data segments, one half are occupied by the datasegments representing the supplemental data inputted to the VSBsupplemental data processor 100. One of the supplement data segment maybe used to transmit the multiplexing information for use by the VSBreception system.

FIG. 6 illustrates an example of inserting the repetition bit into thesupplemental data by the repetition coder 13 according to the preferredembodiment of the present invention. The supplemental data having therepetition data inserted therein is transmitted to the VSB receptionsystem.

When 1 byte is input, a repetition bit is inserted as shown to output 2bytes. As shown in FIG., the repeatedly coded additional data are codedto a leed solomon, interleaved, and input (d1 and d0) to the TMC withoutpassing through a randomizer within 8T-VSB transmitting system.Hereinafter, a relation between the repeatedly coded additional data andthe TMC will be explained with reference to FIG. 8.

The VSB transmitter 110 of the present invention is required to haveidentical probabilities of occurrence of the 8 levels, for havingbackward-compatibility with the related art VSB transmission system.Therefore, the presence of the 0's and 1's in the sequence received asthe input signal D0 at the Trellis coder are required to be almost thesame.

FIG. 7 illustrates a block diagram of the data interleaver 12 forinterleaving the supplemental data in FIG. 3. According to the preferredembodiment, a convolutional interleaver may be used as the datainterleaver 12. However, other suitable interleaver, such as a blockinterleaver, known to one of ordinary skill in the art may also be used.

Referring to FIG. 7, the data interleaver 12 has ‘B’ ( preferably 46)branches, and ‘M’ (preferably 4) bytes of unit memory. The datainterleaver 12 may be operative synchronous to a field synchronizationsignal of the VSB transmission system 16. The ‘B’ branches, and the ‘M’bytes of unit memory of the data interleaver 12 may be changed to othersuitable value without deviating from the gist of the present invention.

Because the VSB transmission system 16 already includes a datainterleaver 3, as shown in FIG. 1, the data interleaver 12 in the VSBsupplemental data processor 1100 of FIG. 2 may be omitted if no furtherburst noise performance improvement is required.

FIG. 8 illustrates a trellis coder and pre-coder. In FIG. 8, if 2 bits(d1 and d0) are input, 3 bits (c2, c1, and c0) are output and thenconverted to one of 8 levels in 8 VSB converter. Also, the additionaldata are input to the TMC without passing through the pre-coder. Sincethe output of an interleaver shown in FIG. 7 is a byte unit and isdivided into 4 units (two bits per unit) per one byte and then input tothe TMC. At this time, the input bits d0 and d1 are output as c1 and c2as they are. Bits of the additional data are the same as d0 and d1 asthe additional data passed through the repetition coder. Accordingly,the output of the TMC is represented as one of 4 symbols shown in FIG.2. Also, the receiver detects the repeatedly coded data in advance.Therefore, by using this information, a performance of a slicerpredictor used in a channel equalizer can be improved and trellisdecoding performance can also be improved.

FIG. 9 illustrates a block diagram showing an example of supplementaldata coding according to the preferred embodiment of the presentinvention. Referring to FIG. 9, the supplemental data has a block sizeof 164 bytes. FIG. 9 illustrates the process of coding the supplementaldata packet until the supplemental data packet is provided to themultiplexer 15. This occurs after the supplemental data packet passesthe Reed-Solomon coder 11, the data interleaver 12, the repetition coder13, and the MPEG header inserter 14 in FIG. 3 in succession.

The operation of the VSB supplemental data processor 100 according tothe present invention will be described. According to FIG. 9, aReed-Solomon 20 byte parity is inserted to the supplemental data that is164 bytes long by the Reed-Solomon coder 11. This process changes thesupplemental data into a 184 byte packet. A number of parity bytes mayvary with a number of the supplemental data bytes. For example, if thesupplemental data has 154 bytes, the parity has 30 bytes. At the end,the number of the supplemental data bytes having the parity bytes addedthereto is fixed to be 184 bytes in advance. The supplemental datahaving the parity added thereto is interleaved by the data interleaver12 and provided to the repetition coder 13. The repetition coder 13expands the supplemental data by inserting 92 bytes of the repetitiondata into each of the 92 bytes of supplemental data to provide two 184byte packets of supplemental data, where the 20 parity bytes areincluded in only one of the two 184 byte packets.

Thereafter, the MPEG header inserter 14 inserts 3 bytes of MPEG header,preferably containing the PID, to the front part of each of thesupplemental data packets for backward-compatibility with the relatedart ASTC 8T-VSB transmission system. The multiplexer 15 multiplexes eachof the supplemental data packets from the MPEG header inserter 14 andthe MPEG data received through another route, and transmits themultiplexed data to the VSB transmission system 16. The VSB transmissionsystem 16 codes the multiplexed data and transmits the data to the VSBreception system.

FIG. 10 illustrates a diagram showing another example of coding thesupplemental data. Referring to FIG. 10, 10 bytes of parity bits areinserted into the 82 extra bytes by the Reed-Solomon coder 11, to changethe extra bytes into a 92 byte packet. The number of parity bytes varieswith the number of the supplemental data bytes. That is, if thesupplemental data has 72 bytes, then the parity has 20 bytes. At theend, the supplemental data having the parity added thereto is fixed tohave 92 bytes in advance. The 92 bytes of supplemental data having the10 bytes of parity added thereto is interleaved by the interleaver 12,and provided to the repetition coder 13, and the repetition coder 13expands the supplemental data by inserting 92 bytes of repetition datainto the 92 bytes of supplemental data, to provide a total 184 bytes ofpacket of supplemental data, accordingly each of the 184 bytes ofpackets includes 10 parity bytes.

Similar to FIG. 9, the MPEG header inserter 14 inserts 3 bytes of MPEGheader to the front part of the 184 bytes of supplemental data packetsfor backward-compatibility with the related art ASTC 8T-VSB transmissionsystem, for a total of 187 bytes of data. Finally, the multiplexer 15multiplexes each of the supplemental data packets from the MPEG headerinserter 14 and MPEG data received through another route, and transmitsthe multiplexed data to the VSB transmission system 16. The VSBtransmission system 16 codes the multiplexed data, and transmits thedata to the VSB reception system. At the end, FIGS. 9 and 10 areidentical in that the total number of bytes of the supplemental datahaving the repetition coder inserted thereto is 184, and the totalnumber of bytes of the supplemental data having the MPEG header addedthereto is 187.

As has been explained, the present invention has the followingadvantages. First, supplemental data can be transmitted on the samechannel with MPEG data with the supplemental data multiplexed with theMPEG data.

Second, a backward-compatibility with the conventional ATSC 8T VSBsystem can be sustained. That is, the reception of the MPEG transportdata at the ASTC 8T-VSB receiver is not affected. Third, reliablereception both of the MPEG data and the supplemental data at thereception system is facilitated by using the predefined sequenceinserted in the supplemental data even on a channel with excessiveghost. Fourth, a noise immunity of the supplemental data is enhanced atthe VSB reception system by using the predefined sequence inserted inthe supplemental data. Fifth, transmission of other MPEG data throughsupplemental data path is permitted, which in turn permits reception ofthe MPEG data even in a poor channel state.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the VSB communicationsystem, and the signal format for the VSB communication system of thepresent invention without departing from the spirit or scope of theinvention. Thus, it is intended that the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

1. A VSB transmitter for use with an MPEG data signal and a supplementaldata signal, the VSB transmitter comprising: a VSB supplemental dataprocessor configured to preprocess the supplemental data signal, the VSBsupplemental data processor comprising: a forward error correction coderthat codes the supplemental data signal; a data expander for expandingeach individual byte of the coded supplemental data signal into twobytes of data in succession to generate an expanded supplemental datasignal; a header inserter for inserting a header to the expandedsupplemental data signal; and a multiplexer for multiplexing the MPEGdata signal and the supplemental data signal having the header insertedthereto in at least one of a predetermined multiplexing ratio and unit,wherein the multiplexing unit is a segment, and the multiplexing ratiovaries with amounts of MPEG data packets representing the MPEG datasignal and supplemental data packets representing the supplemental datasignal; and a VSB transmission system connected to the VSB supplementaldata processor for Trellis-coding the multiplexed data signal, and formodulating the Trellis-coded mulitiplexed data signal to form at leastone data field comprising a plurality of segments that includes at leastone segment formed from the supplemental data signal and at least onesegment formed from the MPEG data signal.
 2. The VSB transmitter ofclaim 1, wherein the forward error correction coder is a Reed-Solomoncoder.
 3. The VSB transmitter of claim 2, wherein the supplemental datasignal includes at least one data packet having X bytes and theReed-Solomon coder provides parity bytes of Y bytes, wherein a total ofX and Y bytes is 184 bytes.
 4. The VSB transmitter of claim 3, whereinthe header inserter adds three bytes of header information to the datapacket, wherein the header information contains program identification.5. The VSB transmitter of claim 1, further comprising an interleaverinterleaving the supplemental data signal coded by the forward errorcorrection coder and outputting an interleaved supplemental data signalto the data expander.
 6. The VSB transmitter of claim 5, wherein theforward error correction coder is a Reed-Solomon coder.
 7. The VSBtransmitter of claim 6, wherein the supplemental data signal includes atleast one data packet having X bytes and the Reed-Solomon coder providesparity bytes of Y bytes, wherein a total of X and Y bytes is 184 bytes.8. The VSB transmitter of claim 7, wherein the header inserter addsthree bytes of header information to the data packet, wherein the headerinformation contains program identification.
 9. The VSB transmitter ofclaim 1, wherein the data expander divides each data packet of thesupplemental data signal coded by the forward error correction coderinto a plurality of data packets, and inserts one byte of repetitiondata after each byte of the divided data packets.
 10. The VSBtransmitter of claim 1, wherein the multiplexing ratio of thesupplemental data packets and the MPEG data packets in the multiplexeris one segment to one segment.
 11. The VSB transmitter of claim 1,wherein the multiplexing ratio of the supplemental data packets and theMPEG data packets in the multiplexer is one segment to three segments.12. The VSB transmitter of claim 1, wherein the multiplexer isresponsive to a field synchronizing signal used for synchronizing a dataframe of the VSB transmission system.
 13. The VSB transmitter of claim1, wherein the data field has 312 data segments and one fieldsynchronizing segment.
 14. A VSB supplemental data processor for usewith a VSB transmission system to provide a supplemental data signal andan MPEG data signal thereto, wherein the VSB transmission systemmodulates at least one data field comprising a plurality of segmentsthat includes at least one segment formed from the supplemental datasignal and at least one segment formed from the MPEG data signal, theVSB supplemental data processor comprising: a forward error correctioncoder that codes the supplemental data signal; a data expander forexpanding each individual byte of the coded supplemental data signalinto two bytes of data in succession to generate an expandedsupplemental data signal; a header inserter for inserting a header tothe expanded supplemental data signal; and a multiplexer formultiplexing the MPEG data signal and the supplemental data signalhaving the header inserted thereto in at least one of a predeterminedmultiplexing ratio and unit, wherein the multiplexing unit is a segment,and the multiplexing ratio vanes with amounts of MPEG data packetsrepresenting the MPEG data signal and supplemental data packetsrepresenting the supplemental data signal.
 15. The VSB supplemental dataprocessor of claim 14, wherein the forward error correction coder is aReed-Solomon coder.
 16. The VSB supplemental data processor of claim 15,wherein the supplemental data signal includes at least one data packethaving X bytes and the Reed-Solomon coder provides parity bytes of Ybytes, wherein a total of X and Y bytes is 184 bytes.
 17. The VSBsupplemental data processor of claim 16, wherein the header inserteradds three bytes of header information to the data packet, wherein theheader information contains program identification.
 18. The VSBsupplemental data processor of claim 14, wherein the data expanderdivides each data packet of the supplemental data signal coded by theforward error correction coder into a plurality of data packets, andinserts one byte of repetition data after each byte of the divided datapackets.
 19. The VSB supplemental data processor of claim 14, furthercomprising an interleaver interleaving the supplemental data signal andoutputting the interleaved supplemental data signal to the dataexpander.
 20. The VSB supplemental data processor of claim 19, whereinthe forward error correction coder is a Reed-Solomon coder.
 21. The VSBsupplemental data processor of claim 20, wherein the supplemental datasignal includes at least one data packet having X bytes and theReed-Solomon coder provides parity bytes of Y bytes, wherein a total ofX and Y bytes is 184 bytes.
 22. The VSB supplemental data processor ofclaim 21, wherein the header inserter adds three bytes of headerinformation to the data packet, wherein the header information containsprogram identification.
 23. The VSB supplemental data processor of claim21, wherein the data expander divides each data packet of thesupplemental data signal coded by the forward error correction coderinto a plurality of data packets, and inserts one byte of repetitiondata after each byte of the divided data packets.
 24. The VSBsupplemental data processor of claim 14 wherein the multiplexing ratioof the supplemental data packets and the MPEG data packets in themultiplexer is one segment to one segment.
 25. The VSB supplemental dataprocessor of claim 14 wherein the multiplexing ratio of the supplementaldata packets and the MPEG data packets in the multiplexer is one segmentto three segments.
 26. A method for a supplemental data packets and MPEGdata packets in a VSB transmitter comprising a VSB supplemental dataprocessor and a VSB transmission system, the method comprising:preprocessing the supplemental data packets, the preprocessing thesupplemental data packets comprising: subjecting the supplemental datapackets of preset bytes to a Reed-Solomon coding and adding aReed-Solomon parity data of preset bytes to the supplemental datapackets; interleaving the coded supplemental data packets; expandingeach individual byte of the interleaved supplemental data packets intotwo bytes of data in succession; adding an MPEG header of preset bytesto each one of the expanded supplemental data packets; and multiplexingthe MPEG data packets with the header-added supplemental data packets ata preset multiplexing ratio, wherein the multiplexing ratio varies withamounts of the MPEG data packets and the header-added supplemental datapackets; and Trellis-coding the multiplexed data packets and modulatingthe Trellis-coded multiplexed data packets through the VSB transmissionsystem.
 27. The method of claim 26, wherein the Reed-Solomon parity datais included to only one of the supplemental data packets.
 28. The methodof claim 26, wherein the expanding each individual byte of theinterleaved supplemental data packets comprising: dividing each one ofthe interleaved supplemental data packets into two supplemental datapackets having the same numbers of bytes; and inserting repetition datahaving the same bytes with the interleaved supplemental data packet intoeach one of the supplemental data packets to provide two supplementaldata packets each having the repetition data inserted therein.
 29. Themethod of claim 28, wherein each one of the supplemental data packetshas 184 bytes comprising 92 bytes of supplemental data and 92 bytes ofthe repetition data.
 30. The method of claim 26, wherein the MPEG headeris an identification code for identifying whether the multiplexed datais the supplemental data packet or the MPEG data packet.